Relay ID - engine compartment

mark houghton · 06:28 PM

It's just me again. All this fiddling around with relays yesterday, of which there is one I'm not sure of it's function.

I borrowed the attached picture from another thread, because it just happens to be exactly as my car is set up. Please check me on this:

the yellow relay is the overboost to cut fuel off
the smaller of the two silver box relays is for the delayed ignition shutoff
the larger of the two silver box relays is the rear window defogger
the round black relay is......WHAT?

During my trouble shooting session yesterday (trying to get the pumps to run), once I got everything working I noticed that if I pulled the round black relay the pumps would stop. What is that black bugger for? It seems real strange to have all these redundant relays and switches just to keep fuel flowing: Ignition switch, fuel head control arm micro switch, overboost sensor to ground, yellow relay, this strange black relay, two pump relays up front, and one pump fuse. Too much crap to go wrong.

Chuck Jones · 04-22-2009, 10:34 AM

Hell Mark...the problem is......there' s no engine in that dogone car! Try installing one, then turn on the ignition key and see if it starts. I found that it worked for me.

BTW...went and looked and I have the same round black relay....dunno....put in by the Department of Redundancy Department I guess.

WERK I · WERK I's Garage

Black Relay - The rear window de-icer?

Chuck Jones · 04-22-2009, 10:43 AM

I've got a cabriolet with a plastic rear window and it has the black relay....don't think a defroster would work well in this case.

equality72521 · 04-22-2009, 10:50 AM

I believe it's the oxygen sensor relay.

JBL930 · 04-22-2009, 11:04 AM

Strange, i thought that was the rear fuel pump relay, i guess i was wrong

equality72521 · 04-22-2009, 11:19 AM

Quote:

Originally Posted by JBL930

Strange, i thought that was the rear fuel pump relay, i guess i was wrong

Not sure on the 80's cars but mine has both fuel pump relays up front.

Shadetree930 · 04-23-2009, 08:49 AM

Quote:

Originally Posted by WERK-I

Black Relay - The rear window de-icer?

This is correct per the 1987 wiring diagram for the Heating and Venitaltion System.

Chuck Jones · 04-23-2009, 08:57 AM

I went and pulled the black plastic cover off and looked at the diagram embossed on the back, and it lists a window heating element....but the plastic cover is probably used on all the cars and they didn't make a special one for the cabs....So you folks are most likely correct.

mark houghton · 04-23-2009, 10:01 AM

Quote:

Originally Posted by Shadetree930

This is correct per the 1987 wiring diagram for the Heating and Venitaltion System.

Nope, don't think so. Go out to your own '87, fire it up and pull the black relay (assuming your '87 and mine both have one). I bet the engine dies due to lack of fuel. It stopped my fuel pumps when I pulled mine.

Pelican lists the rear screen defroster relay as that great big hunker silver can as pictured in my original post. I wonder if that's the Heating and Ventilation relay the wiring diagram is referring to. Here's a link with picture from their catalog:
http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=911-615-115-00-M100&catalog_description=Rear%20Window%20Defroster%20Re lay%2C%20%39%31%31%20%28%31%39%37%34%2D%38%39%29%2 0

Thanks everone...so far. Mystery still not solved....

mark houghton · 04-23-2009, 10:14 AM

Quote:

Originally Posted by Chuck Jones

I went and pulled the black plastic cover off and looked at the diagram embossed on the back, and it lists a window heating element....but the plastic cover is probably used on all the cars and they didn't make a special one for the cabs....So you folks are most likely correct.

+1 on the window heat (I think)
You have a plastic fuse box cover? Man, I'm jealous! Mine is MIA.

equality72521 · 04-23-2009, 10:15 AM

Why does it kill the pumps when you pull it though?

mark houghton · 04-23-2009, 10:47 AM

Quote:

Originally Posted by equality72521

Why does it kill the pumps when you pull it though?

I'm refering to the mystery black relay, not the big silver one that I think is for the rear window heating element. And that's the question....why does it (the black relay) kill the fuel pumps, when the two pump relays are in the front fuse box?

Maybe that black relay is tied into the ignition delay relay (the smaller of the two silver cans), because that's what the ignition delay does...kills the pumps but keeps power to the ignition for a couple seconds when you shut down. Perhaps the two work in tandem.

Hell, lots of conjecture....

JFairman · 04-23-2009, 11:16 AM

I used to know what the black one is for and now I've forgotten... great.

i think i have a jpeg diagram in a folder somewhere that would take an hour or so to find because I always get sidetracked looking at all the other interesting porsche pics i've saved from here and rennlist over the years...

getting old sucks

mark houghton · 04-23-2009, 11:33 AM

Quote:

Originally Posted by JFairman

I used to know what the black one is for and now I've forgotten... great.

i think i have a jpeg diagram in a folder somewhere that would take an hour or so to find because I always get sidetracked looking at all the other interesting porsche pics i've saved from here and rennlist over the years...

getting old sucks

Tell me about it! That's why I just must figure this out before I turn 56, for fear of forgetting what I've learned.

If you find that diagram - and it tells us anything we don't already know - then pass it on. Thanks.

Chuck Jones · 02:17 PM

Mark: You're right about the big silver rectangular box....it's missing in my cab...there's just a hole where it usually goes...so cabs don't need a rear window defroster...so they eliminate it from the rear fuse panel....

I'll go out in the garage, fire it up and pull the black relay, then report the results. Sort of like performing braille mechanics.

ADDENDUM: OK, I went out there, started it up and pulled the black relay....nothing happened, put it back in and pulled it again...nothing, but I thought I heard the engine slow down a bit and the smell of unburned gas from the tailpipe made my eyes water a bit......but it's possible that I never gave it time to warm up, so it might have some nexus to some part that richened up the AFRs....dunno....I'm shooting blind here....but the car definitely didn't stop, however I didn't let it run on to see if it eventually died.

A930Rocket · 04-23-2009, 02:55 PM

I'm 50 and getting old enough to swear that's a pic of my car in my old garage.

Is that your car?

Quote:

Originally Posted by mark houghton

Tell me about it! That's why I just must figure this out before I turn 56, for fear of forgetting what I've learned.

If you find that diagram - and it tells us anything we don't already know - then pass it on. Thanks.

mark houghton · 04-23-2009, 03:27 PM

Quote:

Originally Posted by A930Rocket

I'm 50 and getting old enough to swear that's a pic of my car in my old garage.

Is that your car?

HA! I wondered when/if you would catch that. That IS your car, I believe. I picked the picture from an older thread as I was researching, because it matched what I have on mine.

Thanks for the picture, and no you're not getting Alzheimers yet.

Chuck Jones · 04-23-2009, 09:25 PM

Mark: I was going thru the eBay Porsche 930 stuff and saw the plastic fuse cover on there that looks a lot like mine....but you have to check out item # 370191662758. It even has the wing nuts for securing it....hope this fits yours, then you won't be jealous anymore.

Chuck

Turboo934 · 03:08 AM

That black relay should be red. It runs the micro switch on the fuel head.But my car's a 76 I could be wrong though, for the later 930's.